Indicator tube having auxiliary electrodes for maintaining cathode glow



Nov. 25, 1969 FE L 3,480,820

INDICATOR TUBE HAVING AUXILIARY ELECTRODES FOR MAINTAINING CATHODE GLOW Filed Sept. 8, 1967 2 Sheets-Sheet 1 FIG! Io FIG.2

l NVENTOR.

RICHARD B. F EHNEL wom Nov 25, 1969 R. a. FEHNEL 3,480,820

INDICATOR TUBE HAVING AUXILIARY ELECTRODES FOR MAINTAINING CATHODE GLOW Filed Sept. 8, 1967 2 Sheets-Sheet 2 FIG. 6-

INVENTOR.

RICHARD B. FEHNEL MW-w United States Patent 0.

U.S. Cl. 313-1095 1 Claim ABSTRACT OF THE DISCLOSURE The disclosure is of an indicator tube having a plurality of glow cathodes in a gas-filled envelope and including an auxiliary electrode arrangement for facilitating ionization of the gas and producing cathode glow.

Background of the invention Indicator gas tubes including a plurality of glow cathode electrodes of the type known as Nixie tubes have been made and sold for a considerable length of time by Burroughs Corporation. Generally, in this type of tube, the application of a suitable potential between a glow cathode and another electrode, known as an anode, causes a sheath of gas around the selected cathode to ionize and glow, and the cathode itself appears to glow. It is well known that a finite time is required after the selected potentials are applied before the gas ionizes and the cathode glows. It is also known that, when such tubes are used in the dark or in certain circuit applications, the ionization time is increased, and, for some applications, this increased ionization time is undesirable.

Summary of the invention Briefly, according to the present invention, a multiple cathode gas indicator tube is provided with an auxiliary electrode arrangement which, in eifect, serves to provide a source of electrons and reduce cathode ionization time. The arrangement comprises essentially an auxiliary anode and cathode which are arranged to glow constantly and thus maintain a portion of the gas content of the tube ionized.

Description of the drawing In the drawing:

FIG. 1 is an isometric view of the front of an indicator tube embodying the invention;

FIG. 2 is an isometric view from the rear of the tube of FIG. 1;

FIG. 3 is an enlarged view of a portion of the tube of FIG. 1;

FIG. 4 is an enlarged view of a portion of FIG. 3;

FIG. 5 is a plan view of some of the features of the tube of FIG. 1; and

FIG. 6 is a perspective view of a cathode electrode and a mounting arrangement therefor.

Description of the preferred embodiment For purposes of illustrating the invention, a side-view indicator tube 10 is shown. In such a tube, the cathodes are viewed through the side Wall of the tube envelope. However, the universality of the principles of the invention will be clear to those skilled in the art.

Referring to the drawing, the indicator tube 10 embodying the invention includes an envelope 20 which contains a gas suitable for supporting cathode glow, such as argon, neon, or the like. If desired, other substances such as mercury may be added in small quantities to the gas con tent of the envelope.

The envelope 20 is generally vertically elongated and its side wall 22 comprises a viewing window. The envelope 3,480,820 Patented Nov. 25, 1969 includes a base or stem 24 through which a plurality of metal pins 28 extend and to which the cathode electrodes 30 are connected so that operating potentials can be applied to them. The tube envelope includes the usual tubulation 32 which may be provided in the dome of the envelope, as shown, or it may be in the stem 24. Pins 28 extend to about the same height within the envelope; however, several other pins, for example, pins 34, 35, 37 and 38, are somewhat longer and carry glass sleeves 39 on which a mica support disk 44 is supported. Pins 34, 35, and 36 are positioned at the rear of the stem, and pins 37 and 38 are positioned at the front of the stem. The various tube pins may be arrayed in the stern in any suitable manner consistent with their function, and other pins may also be used to support mica disk 44. Pins 34 and 35 also extend through suitable apertures in the mica plate 44 and extend above the mica plate a convenient distance. The plate 44 also includes either an elongated central slot 48 or a plurality of holes to permit cathode leads 49 to run from the cathodes 30 to the tube pins 28. The spacing of mica plate 44 above pins 28 facilitates the dress of the cathode leads beneath the mica plate.

The electrode assembly in tube 10 includes an anode structure 50 which comprises a solid rear plate 52 and a front mesh screen 54 which faces the viewing window 22 of the tube. The anode back plate and front screen have side panels which meet to form a continuous generally hollow tubular anode chamber in which the cathode electrodes 30 are positioned. The anode plate and screen are seated on the bottom mica plate, and are secured to it and to an upper mica plate 56 by the usual tabs 58. Bottom tabs are not shown. The rear anode plate 52 is also welded to pin 34 for rigidity and to provide means for connecting anode potential thereto. The glass sleeve 45 on this anode pin 34 shields the pin from the adjacent. cathode pins 28.

A pair of cathode support posts including an upper support post 60 and a lower support post 64 are secured between the front screen 54 and rear anode plate 52. The posts 60 and 64 are either made of an insulating material such as a ceramic, or they are made of metal and are coated with glass or carry a glass sleeve to provide the required insulation for the cathode electrodes 30 which are supported thereon. The support posts may be secured to the anode screen and plate by welding or by means of eyelets 68 crimped to the ends of the posts extending through apertures in the plate and screen.

The electrode assembly also includes a plurality of cathode electrodes 30 which are in the form of characters, usually numerals. To simplify the drawing, cathode electrodes are not shown in each figure, and only one cathode is shown FIGS. 2 and 6. However, usually ten cathode numerals 0 to 9 are provided. The cathode electrodes are of metal such as stainless steel, nickel, molybdenum, or the like, and they are provided with apertured mounting tabs at opposite ends. The tabs may be generally U-shaped or annular (FIG. 6), and they serve to support the cathodes on support posts 60 and 64. The cathodes are insulated from each other by means of insulating washers 84 which are threaded on the support posts between the cathodes. If desired, one or more auxiliary electrodes, which may be duplicate cathode numerals, may be mounted at different locations along the stack of cathode electrodes :for operation as anodes.

Each cathode is provided with a cathode lead 49 for making electrical connection to one of the tube pins 28. This lead may be an integral extension from the lower mounting tab 80 of each cathode as shown in FIG. 6, or it may be a separate lead having its own apertured tab (like cathode tab 80), by means of which it is threaded on the lower support post and positioned between each cathode and an insulating spacer 84. This arrangement is not shown in the drawings. The cathode leads 49 are usually welded to pins 28.

According to the invention, the tube includes an assembly for facilitating ionization of the gas and cathode glow. This assembly is positioned behind the rear anode plate 52 and is built on tube pins 35 and 36. Since, in this arrangement, tube pin 35 is to carry anode potential in operation, it is provided with a glass sleeve 100 which is of sufiicient length to rise above the upper end of pin 35. Glass sleeve 45 for supporting mica disk 44 surrounds glass sleeve 100. A relatively strong, rigid, insulated lead wire 104 is welded to pin 35 and extends out of the glass sleeve 100, and its free end carries a metal disk 108 welded thereto. The wire 104 is bent so that disk 108 is positioned above pin 35 at a convenient height above mica disk 44. The disk 108 thus comprises an auxiliary anode, and an auxiliary cathode is provided for operation with it which comprises a metal disk 112.

The cathode disk 112 is seated on a ceramic washer 116 Which is seated on the mica disk 44. A connecting conductive lead 118 extends from cathode disk 112 through Washer 116 and a suitable aperture 117 in the mica disk to a connection to pin 36. If desired, pin 36 may be of sufiicient height for disk 112 to be welded directly to it. The seating of disk 112 directly on ceramic washer 116 and the covering of aperture 117 by disk 112 prevent the spread of sputtered cathode material from disk 112 down to pin 36. Cathode disk 112 and anode disk 108 prefererably face each other at the same height and positioned close together.

It is clear that, when tube 10 is placed in operation, the electrode functions could be reversed and electrode 108 could be the cathode and electrode 112 could be the anode. For this reason, it would be desirable to provide pin 36 with a glass sleeve 45.

For optimum operation and long life, the tube 10 includes in its atmosphere a small quantity of mercury vapor which serves to minimize cathode sputtering during tube operation. The mercury may be provided in any suitable fashion. For example, it may be introduced directly with the tube gas or gases, or it may be released, by heating, from a capsule 130 suitably mounted in the envelope.

In operation of the tube 10, and particularly the auxiliary anode 108 and cathode 112, the usual anode-tocathode potential difference of say, 170 volts is applied between them. This potential causes current to flow between the anode and cathode disks and the gas surrounding the cathode disk is ionized and is caused to glow. But, since the auxiliary anode 108 and cathode 112 are positioned behind the solid rear anode plate 52 and they are small in area, they are shielded from view and their glow is not visible in normal use of the tube. However, since the gas is ionized between auxiliary anode and cathode, these ions facilitate the glow of the cathode numerals 30 when glow potentials are applied between the anode cylinder 50 and one of these cathode numerals. It has been found that, in indicator tubes of the prior art, ionization time might range from ten milliseconds in normal ambient light to as much as one second in the dark, while tubes embodying the invention ionize and cathode glow is obtained in less than one hundred microseconds.

What is claimed is:

1. A cathode glow indicator tube including an envelope filled with an ionizable gas capable of sustaining cathode glow and having a stem,

said envelope having a viewing window,

a stack of cathode electrodes mounted within said envelope for viewing through said viewing window,

a generally tubular anode electrode enclosing at least a portion of said stack of cathode electrodes and including a solid plate portion which is positioned behind said stack of cathode electrodes remote from said viewing window,

an auxiliary small anode electrode and an auxiliary small cathode electrode positioned remote from said viewing window hidden by said anode and adapted to be energized at all times to provide a source of electrons for said cathode electrodes,

a plurality of tube pins sealed in said stem and accessible both inside and outside said envelope,

a mica disk supporting said anode electrode and said stack of cathode electrodes,

said mica disk being seated on glass sleeves which are mounted on a plurality of said tube pins for support,

one of said tube pins extending through said mica disk behind said solid anode plate and making electrical contact with said solid anode plate,

another tube pin extending through said mica disk behind said solid anode plate,

a glass sleeve enclosing said other tube pin and extending above the upper end thereof,

an insulated lead secured to said other tube pin and extending out of said glass sleeve and carrying said auxiliary anode electrode at its free end,

said auxiliary cathode electrode being mounted adjacent to said auxiliary anode electrode and supported on said mica disk, and

a lead extending from said auxiliary cathode electrode through an aperture in said mica disk to a tube pin,

said auxiliary anode and cathode electrodes comprising small-area metal disks positioned close together and facing each other.

References Cited UNITED STATES PATENTS 1,955,391 4/1934 Schroter 313-189 2,756,366 7/1956 Maynard 315-334 2,917,651 12/1959 Schagen 313-210 2,996,635 8/1961 Klepp et al 313-1095 3,005,922 10/1961 Hart 313-1095 3,242,370 3/ 1966 Milliken 313-210 X 3,242,378 3/1966 Kobayashi 313-189 X 3,262,010 7/1966 Kazan 313-1095 X 3,358,176 12/1967 Rosenberg et al. 313-210 X ROBERT SEGAL, Primary Examiner US. Cl. X.R. 313l89 

